Heavy work vehicles are known, used in the building trade, normally consisting of a truck on which an extendible arm is mounted, and/or telescopically extendible, articulated to distribute and cast concrete. The trucks may be equipped with concrete mixers or not.
Extendible arms of a known type consist of a plurality of segments pivoted to each other and foldable on each other, so as to be able to assume a folded configuration close to the truck, and a working configuration in which they are extended one with respect to the other and allow to reach areas very far from the truck.
One of the most important characteristics of these extendible arms is their ability to reach the greatest heights and/or lengths possible, so as to be able to guarantee maximum flexibility and versatility of use with the same truck.
The increase in the number of articulated segments, or the extension in measurement of each of them, on the one hand entails the possibility of obtaining greater overall lengths in maximum extension, but on the other hand entails an increase in the weights and bulk which are not compatible with current legislation or with the operativeness and functionality of the vehicle.
It is also known that a very serious disadvantage for the correct effectiveness of these arms, which increases as the overall length of the arm and the number of its segments increase, is the phenomenon of vibrations to which the arm is subject as the concrete is distributed. These vibrations entail considerable operating difficulties both for the operator in charge of manually positioning and directing the tube from which the concrete exits, and also for the operator who moves the arm by means of remote control.
An important component of the vibrations also derives from the type of these machines and their characteristics of slimness, their inertial and elastic properties, and the type of construction. These characteristics induce dynamic stresses into the articulated arm which are associated both with the motions of the machine, in a substantially static condition or in any case when it is not pumping, and also with the dynamic loads associated with the pumping step of the concrete.
In fact, for use, the machine always has to act in transitory conditions between one placement and the next, or during its movement; this implies that its motion is continuously excited and dynamic variations are generated on the state of stress of the joints and in the material, which limits the working life of the machine and reduces safety for the operators.
Furthermore, to these effects are added the forced pulsating functioning associated with the piston pump used to pump the concrete, which often occurs at frequencies near the frequencies of the machine itself.
A known device which has the function of damping the vibrations of an articulated arm is described in U.S. Pat. No. 7,143,682. In this known device a compensation mechanism is provided, on the side of the drive system, to compensate a disturbance which has determined a movement of the arm with respect to the position envisaged: the disturbance may consist for example of the fluctuations in pressure at which the concrete is delivered.
The teaching of U.S. Pat. No. '682 is specifically directed to the uncontrolled movements of the arm, or of one or more of its segments, that are generated during the phase of delivery of the concrete, particularly due to the cyclical loads to which the concrete distribution arm is subjected in the phase of delivery and which have the effect of making the entire arm perform a vibration motion. Moreover, this document does not provide to built and use a theoretical numerical model able to represent the condition of the arm and/or of its segments when it/they is/are subjected to the movement by the operator to move the arm in the position of delivery of the concrete before starting the concrete delivery step.
Other devices to control and compensate the vibrations of an articulated arm are described in JP 7133094 and JP 2000-282687.
These known devices, however, are to be considered in practice not totally satisfactory, since their intervention logic is limited to correcting the vibration at the point where it is detected, trying to compensate it with a localized correction intervention without intervening actively on the general structure of the arm considering the various components that cause the vibration.
Purpose of the invention is therefore to obtain a perfected method of active control of the vibrations of an articulated arm, which allows to correct and compensate the vibrations.
The Applicant has devised, tested and embodied the present invention to obtain this purpose, and other advantages described hereafter.